Institut für Nutzpflanzenwissenschaften und Ressourcenschutz (INRES) Bodenwissenschaften The role of abiotic processes in the formation and degradation of gaseous nitrogen compounds in the soil Inaugural-Dissertation zur Erlangung des Grades Doktor der Agrarwissenschaften (Dr. agr.) der Landwirtschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vorgelegt von Jannis Heil aus Essen Bonn 2015 Referent: Prof. Dr. Nicolas Brüggemann Korreferent: Prof. Dr. Wulf Amelung Tag der mündlichen Prüfung: 10.08.2015 I Contents Acknowledgements ..................................................................................................................... IV Abstract ......................................................................................................................................... V Zusammenfassung ...................................................................................................................... VII List of Figures ............................................................................................................................. IX List of Tables ............................................................................................................................... XI List of abbreviations ................................................................................................................... XII 1. Introduction .............................................................................................................................. 1 1.1. Rationale ............................................................................................................................ 2 1.2. Objectives and outline of the thesis ................................................................................... 5 2. A review of chemical nitrogen trace gas formation reactions of nitrification intermedi- ates in soils ..................................................................................................................................... 9 2.1. The role of nitrification intermediates in abiotic nitrogen trace gas formation ............... 10 – 2.2. Accumulation of NO2 ..................................................................................................... 12 2.2.1 Role of soil properties .......................................................................................... 12 2.2.2 Agricultural practices ........................................................................................... 13 2.2.3 Drying/rewetting in seasonally dry ecosystems ................................................... 14 2.3. Abiotic N trace gas production mechanisms .................................................................... 15 – 2.3.1 Self-decomposition of NO2 ................................................................................. 15 – 2.3.2 Reactions of NO2 with metals ............................................................................. 17 – 2.3.3. Reactions of NO2 with SOM ............................................................................. 20 2.3.4. Reactions involving hydroxylamine ................................................................... 23 2.4. Implications of abiotic processes in terrestrial N trace gas emissions ............................. 27 2.5. Outlook ............................................................................................................................. 30 15 3. Site-specific N isotopic signatures of abiotically produced N2O ...................................... 32 3.1. Introduction ...................................................................................................................... 33 3.2. Materials and Methods ..................................................................................................... 34 II 3.2.1. Preliminary experiments ..................................................................................... 34 3.2.2. Laboratory setup for isotope-specific N2O measurements .................................. 35 3.2.3. Instrumentation ................................................................................................... 38 3.3. Results .............................................................................................................................. 39 – 3.3.1. NO and N2O production from nitrification intermediates NH2OH and NO2 ..... 39 3.3.2. Isotopic signatures of abiotically produced N2O ................................................ 41 3.4. Discussion ........................................................................................................................ 45 – 3.4.1. NO and N2O production from nitrification intermediates NH2OH and NO2 ..... 45 3.4.2. Comparison of reaction mechanisms .................................................................. 46 3.4.3. Comparison with other studies ............................................................................ 48 3.4.4. Mechanism leading to high positive SP .............................................................. 48 3.4.5. Source partitioning .............................................................................................. 49 3.5. Conclusions ...................................................................................................................... 50 4. Abiotic N2O production from hydroxylamine in soils and their dependence on soil properties ..................................................................................................................................... 52 4.1. Introduction ...................................................................................................................... 53 4.2. Material and methods ....................................................................................................... 54 4.2.1. Sample collection ................................................................................................ 54 4.2.2. Soil chemical analyses ........................................................................................ 55 4.2.3. Incubation experiments ....................................................................................... 55 4.2.4. Reaction kinetics analyses .................................................................................. 57 4.2.5. N2O isotopic analyses ......................................................................................... 58 4.2.6. Calculations ......................................................................................................... 59 4.3. Results .............................................................................................................................. 59 4.3.1. Soil incubation experiments ................................................................................ 59 4.3.2. Kinetics of N2O formation .................................................................................. 62 4.3.3. Isotopic signature of produced N2O .................................................................... 64 4.4. Discussion ........................................................................................................................ 65 4.4.1. Abiotic N2O formation from different soils ........................................................ 65 4.4.2. Factors influencing abiotic N2O formation ......................................................... 67 4.4.3. Isotopic signature of abiotically produced N2O .................................................. 70 4.5. Conclusions ...................................................................................................................... 70 5. N2O decomposition over hot and dry surfaces ..................................................................... 72 5.1. Introduction ...................................................................................................................... 73 III 5.2. Materials and Methods ..................................................................................................... 74 5.3. Results .............................................................................................................................. 76 5.4. Discussion ........................................................................................................................ 79 5.5. Conclusions ...................................................................................................................... 81 6. Synopsis ................................................................................................................................... 82 6.1. Summary .......................................................................................................................... 83 6.2. Synthesis .......................................................................................................................... 86 6.3. Perspectives ...................................................................................................................... 89 6.3.1. Source partitioning using stable isotopes ............................................................ 89 6.3.2. Abiotic NH2OH oxidation in soils ...................................................................... 90 6.3.3. N2O decomposition over hot and dry surfaces ................................................... 91 References ................................................................................................................................... 92 IV Acknowledgments